The theory of the evolution of human's ancient ancestors may have become significantly "simplified." As a result of archeological discoveries made in Georgia, scientists now estimate that the number of different species previously thought to make up our ancient ancestors may in fact all belong to the Homo erectus species. To prove that theory, scientists have used a particularly well-preserved skull – named simply "Skull 5" – that was discovered, along with four others, in Dmanisi, Georgia.
In an article published in Science magazine, David Lordkipanidze, Director of the Georgian National Museum in Tbilisi and the lead author of the study, and Christoph Zollikofer, a neurobiologist at the Anthropological Institute and Museum in Zurich, declare that Homo habilis, Homo rudolfensis and Homo erectus, each previously thought to be separate species, in reality, represent variations within a single specimen of hominids.
The skull discovered in Dmanisi is presumably an early form of Homo erectus. This species, which emerged in Africa 1.8 million years ago, had proportions similar to a modern human and is assumed to be the first species that applied fire to cook food.
Skull 5 was first discovered in 2005, years before that, in 2000, archeologists found a jawbone of a female at the same site. The article published in Science informs us that the skull belonged to the adult male who had a large, long face with heavy features, a large jaw with teeth, but an exceptionally small braincase (only 550 cubic centimeters). The skull was compared with the skulls of other species of the Homo genus found in Africa.
The other four skulls discovered are thought to belong to an elderly toothless male; another middle aged male; a young female and an adolescent of unknown sex. The scientists do not know whether the four belonged to the same family or even whether they lived at the same time.
Each of the five hominids might have been dragged into the den of a predator; with the den then caving in, preserving the skulls intact.
By employing dating technology based on argon isotopes, the archeologists established that they lived between 1.77 and 1.85 million years ago.
"Dmanisi is a unique snapshot of time – maybe a time capsule that preserves things from 1.8 million years ago," Professor David Lordkipanidze said. The skulls of human ancestors found in Dmanisi are, after those in Africa, the second oldest ever to be found.
"This was a place where there was big competition between carnivores and hominids. It seems that they were fighting for carcasses and, unfortunately for the hominids, but fortunately for us, they were not always successful," said Lordkipanidze.
Each of the five skulls unearthed in Dmanisi significantly differed from each other physically. According to the scientists working on the site, had those skulls been found at various places in Africa, they would have been attributed to different species. However, study of those five skulls revealed that they lived in the same location and belonged to the same species.
"The five skulls from Dmanisi look quite different from one another, so it's tempting to publish them as different species. Yet we know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species," Professor Zollikofer said.
The researchers have asserted that despite their anatomical differences, 3D modelling of the five skulls has shown that they differed from one another as much as five modern humans or five chimpanzees would vary from one another.
Professor Ian Tattersall of the American Museum of Natural History in New York believes that the fifth skull from Dmanisi is "undoubtedly one of the most important ever discovered." An opinion is shared by Professor Tim White of the University of California, Berkeley, who said that the significance of the discovery is immense, describing the skull as "an iconic fossil."
The new discovery of the team led by Professor Lordkipanidze raises questions about a species called Australopithecus sediba that lived in South Africa some 1.9 million years ago. According to existing theories, this creature was seen as a direct ancestor of modern humans. The scientist behind this claim, Lee Berger from the University of Witwatersrand, declared that it is too premature to dismiss his findings and criticizes Lordkipanidze's team for failing to compare their skulls with the remains of Australopithecus sediba.
A number of paleontologists are skeptical about the Dmanisi discovery. Professor Fred Spoor of Germany's Max Planck Institute for Evolutionary Anthropology asserts that the methodology applied by the researchers is not efficient enough to claim that all five skulls belonged to a single species. According to him, the research is largely based on a very general shape analysis of the cranium – capable of describing the shape of a face but insufficient to determine species. Spoor notes that the study does not use those critical distinct characteristics of Homo erectus, Homo habilils or Homo rudolfensis (for example, the existence of long arms) that would distinguish them from other species. In his opinion, the Dmanisi skull is, nonetheless, certainly an important discovery and, in terms of evolution, must be placed between Homo habilis and Homo erectus.
David Lordkipanidze responded to Spoor's criticisms in an interview with the Georgian internet edition, Netgazeti. According to Lordkipanidze, Spoor has not probably read his paper to the end because it contains additional materials. As Lordkipanidze says, Spoor is just defending the position of his team that favors the theory of a variety of species.
"There is a dual methodology. The first is shape, the classical method. The second is size and measurement, for which we already use the modern methodology of computer paleontology. Both the shape and measurements are compared. For comparison we took a huge amount of statistical data on modern humans and apes and, of course, on fossils. The variations are important, for example in the size of braincase – in the Dmanisi fossils we established the size of one as 550 whilst another as 750 cubic centimeters," Lordkipanidze told Netgazeti.
Professor Chris Stringer of the Natural History Museum in London acknowledges that the team of Dmanisi researchers has indeed discovered a new type of skull, but he is still skeptical about the theory that all hominids belong to one species.
"Only H. erectus survives and becomes successful but at the origin, nature was experimenting with how to evolve humans in terms of increasing brain size," he told the BBC. "Creatures were starting to use tools and eat meat, and this drove evolution, but I think it also drove diversity. The Dmanisi group is an example of the successful species that came out of that and then carried on to spread around the old world," said Professor Stringer.
Through observation of the same skulls, David Lordkipanidze, Christoph Zollikofer and a researcher Ana Margvelashvili have also established that the ancient ancestors of modern humans even cleaned their teeth. They detected traces of their having used toothpicks and signs of diseases resulting from that.
"The key significance of Dmanisi is that the most well-preserved sample has been discovered, giving a possibility to study not only isolated fossils but also the entire group, a population. This provides the opportunity to undertake a population biology study of earlier Homo," Lordkipanidze said.
|Homo sapiens: Modern humans, the only species that survived out of the Homo genus. Period of existence: from 200,000 years ago to present.|
|Homo neanderthalensis: Place of discovery: Neander's Valley, Germany. Is considered either as a variety of the Homo sapiens species or a separate species. Period of existence: 300,000-30,000 years ago (650,000 years ago for proto-Neanderthals). Several theories for the extinction of the Neanderthals exist: 1. Neanderthals were a separate species and the birth of modern humans, Homo sapiens, and a conflict with them caused their extinction; 2. Neanderthals were a subspecies of Homo sapiens and disappeared through absorption; 3. Climate change.|
|Homo heidelbergensis: Places of discovery: Germany, Europe, and Africa. Period of existence: 250,000-200,000 years ago. Believed to be an ancestor of the African Homo sapiens and European Neanderthals.|
|Homo antecessor: Place of discovery: Spain. Period of existence: 600,000-250,000 years ago.|
|Homo erectus: Places of discovery: Africa, Georgia, Spain, England, India, Sri Lanka, and China. Period of existence: 1.8 million-143,000 years ago. The skull first discovered in Dmanisi in 1991 was initially called Homo erectus georgiсus. According to the first evaluation, he was supposed to be a descendant of Homo habilis and an ancestor of Homo erectus. Later, however, it was established that it belonged to the Homo erectus species. According to one theory, Homo erectus originated in the Caucasus and migrated from there to Africa and other territories. According to another, more popular theory, Homo erectus migrated from Africa and via the modern territory of Dmanisi to the rest of Eurasia.|
|Homo floreniensis: Nicknamed "hobbit." Place of discovery: Indonesia. Period of existence: 94,000-12,000 years ago.|
|Homo ergaster: Place of discovery: Eastern Africa. Period of existence: 2.33-1.44 million years ago.|
|Homo habilis: Place of discovery: Tanzania. Period of existence: 2.33-1.44 million years ago.|
|Homo rudolfensis: Place of discovery: Kenya. Period of existence: 2 million years ago. A contemporary specimen of Homo habilis.|